Characterisation of hCG responses and LH/CGR action in the human endometrium

Abstract

Human endometrial stromal cells (HESCs) undergo cyclic differentiation, termed decidualisation, into highly specialised cells, which prepares them to respond appropriately to embryonic signals and this is critical to facilitate successful implantation. Human chorionic gonadotrophin (hCG) is secreted by the embryo and is known classically to maintain progesterone production from the corpus luteum during early pregnancy yet emerging evidence reports that it signals in a paracrine manner at the embryo-endometrial interface. Its cognate receptor, the LH/CGR, is a G-protein coupled receptor (GPCR) that is expressed in the endometrium but the role of hCG and its underlying signalling mechanisms here are largely unknown. I show that in HESCs hCG acts via a non-classical Gαi pathway and that signalling via this pathway can negatively regulate important decidua-specific genes. Furthermore, the LH/CGR undergoes ‘reprogramming’ during decidualisation, which changes both its trafficking and MAPK signalling profiles, where only a subset of pathways are activated by hCG upon decidualisation. I further show that the majority of the LH/CGR localises to an endocytic compartment which is distinct from the early endosome, termed the very early endosome (VEE) and that this is dependent on the C-terminal tail of the receptor. Moreover, cellular depletion of an essential VEE component, GIPC, can cause hCG-induced modulation of downstream decidual genes to be reversed. Importantly, in HESCs from recurrent miscarriage (RM) patients, hCG-induced signalling opposes that of signalling in control patients and in addition, LH/CGR trafficking and recycling may be disordered. Together, these findings provide novel insights of the mode of action of hCG and the LH/CGR in the endometrium and highlight how perturbation of their signalling and trafficking profiles may contribute to pregnancy loss.